Capacitor array and method of manufacture

ABSTRACT

An improved array of capacitors is provided wherein the improvement includes improved electrical properties and improved packing density. The array has an anode foil and a dielectric on a surface of the anode foil. A multiplicity of areas are defined on the dielectric wherein each area is circumvented by an isolation material and the isolation material extends through the dielectric. A conductive cathode layer in each area forms a capacitive couple. At least one substrate vacancy is in the anode foil and the substrate vacancy electrically isolates adjacent anodes of adjacent capacitive couples. A carrier film is attached to the capacitive couples.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention claims priority to U.S. Provisional ApplicationNo. 61/764,667 filed Feb. 14, 2013, which is incorporated herein byreference.

BACKGROUND

The present invention is related to an improvement in capacitor arraysand to an improved method for making capacitor arrays.

Miniaturization is an ongoing desire in the electronics industry. Thisdesire is driven by consumer demands for smaller, more functional,devices with decreased size and weight. This demand is contrary to thedemand for decreased cost.

A perplexing problem, which is inherent in miniaturization, is theincrease in parasitic electrical characteristics that plague circuitry.Even as components themselves can be improved there are physicalbarriers when these components are attached to a circuit board thatnegate some of the electrical improvements provided by the discretecomponents themselves. Related specifically to the issues of parasiticelectrical characteristics, as discrete components, capacitors aretypically attached individually to a circuit or package and whenattached they require two things; space and electrical connection. Ascomponents become smaller the space between them to account for handlingcapabilities, and tolerances, to ensure they do not touch become a largepercentage of the total circuit footprint. This introduces poorefficiency in space utilization and causes unwanted electricalperformance. Prior teachings, such as commonly assigned U.S. Pat. No.7,745,281, which is incorporated herein by reference, create advantagesin the performance of capacitor miniaturization and manufacturing. Whilethis art teaches methods for creating capacitors capable of beingembedded, and capacitor manufacturing methods that include forminggroups of discrete capacitors, it is the purpose of this invention toteach methods that utilize miniaturization techniques to createusefulness while avoiding many of the described issues that arise withdiscrete capacitors.

As the part size decreases, the manufacturing system necessary to placea large number of very small parts on a circuit becomes more complex asdoes the equipment required to bond the component to a circuit. Theincreased handling complexity can easily result in cost increases whichcould be many multiples above the material savings gained through theminiaturization. Related to the issue of cost, handling individualcomponents requires expensive equipment. This cost is multiplied whenthe need to handle large quantities of components is complicated by theever increasing desire to increase the handling speed of the components.Methods of creating arrays of capacitors have been seen in prior art andexist as industry practices as taught by Donghang in U.S. Pat. No.6,324,048, which is incorporated herein by reference. These techniquescan be used to create arrays and groups of capacitors but thesecapacitors are of very low capacitance. It will be the purpose of thisinvention to differentiate from these methods by the use of valve metaland the techniques to create close packed arrays of high capacitancecapacitors.

The instant invention addresses ways of avoiding some of the priorpitfalls in miniaturization technologies, specifically those whichrelate to non-discrete capacitors, more specifically, but not limitingto the scope of this invention, valve metal capacitors that fit thecriteria of being embeddable or incorporated into packaging or substratewhich houses more than just discrete capacitors or capacitor elements.While the term embedded in the industry, specifically capacitors,describe a capacitor that is incorporated into a substrate, typically aprinted circuit board, for purposes of simplification in the presentinvention the term should be understood to include any capacitor devicethat is incorporated into another package or substrate, with or withoutits own packaging.

Capacitor arrays have been described in the art with the cathodecomponent being formed within isolation areas or dams. As the demand forfurther miniaturization has continued the electrical parasitics in suchdevices has proven to be detrimental. It has now been determined thatthe prior art devices exhibit migration, or wicking, of cathodecomponents under the insolation dams thereby resulting in the formationof electrical parasitics which limited the minimum size available.

The present invention provides an improved capacitor array whereinparasitic electrical characteristics can be minimized thereby allowingfor closer packing. The present invention also provides an improvedmethod for manufacturing an array of capacitors.

SUMMARY

It is the objective of this patent to provide an improved capacitorarray and an improved method for manufacturing a capacitor array.

A particular feature of the invention is the ability to providecapacitors in an array thereby mitigating the manufacturing difficultiesassociated with handling individual capacitors.

Yet another feature of the instant invention is the minimization ofparasitic electrical properties typically associated with currentplacement capabilities of discrete components and allowing for higherdensity of discrete capacitors.

These and other advantages, as will be realized, are provided in anarray of capacitors. The array has an anode foil and a dielectric on asurface of the anode foil. A multiplicity of areas are defined on thedielectric wherein each area is circumvented by an isolation materialand the isolation material extends through the dielectric. A conductivecathode layer in each area forms a capacitive couple. At least onesubstrate vacancy is in the anode foil and the substrate vacancyelectrically isolates adjacent anodes of adjacent capacitive couples. Acarrier film is attached to the capacitive couples.

Yet another embodiment is provided in a method of forming an array ofcapacitors. The method includes:

forming a dielectric layer on a surface of an anode foil;

forming areas on the anode foil wherein each area is circumvented byisolation material and the isolation material extends through thedielectric;

forming a conductive cathode layer inside each area thereby formingcapacitors;

applying a carrier film to the capacitors;

removing at least a portion of the anode foil to electrically isolatedadjacent capacitors.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a top schematic view of an embodiment of the invention.

FIG. 2 is a partial cross-sectional schematic view, taken along 2-2 ofFIG. 1

FIG. 3 is partial cross-sectional schematic view of an embodiment of theinvention.

FIG. 4 is partial cross-sectional schematic view of an embodiment of theinvention.

FIG. 5 is partial cross-sectional schematic view of an embodiment of theinvention.

FIG. 6 is partial cross-sectional schematic view of an embodiment of theinvention.

FIG. 7 is partial cross-sectional schematic view of an embodiment of theinvention.

FIG. 8 is partial cross-sectional schematic view of an embodiment of theinvention.

FIG. 9 is top schematic view of an embodiment of the invention.

FIG. 10 is top schematic view of an embodiment of the invention.

DESCRIPTION

The present invention is directed to improved capacitors, andparticularly, capacitors which can be formed in very dense arrays forsingulation or to be utilized as an array of capacitors. The presentinvention is also directed to a method of forming an array of capacitorswith decreased electrical parasitics and a higher packing density thanpreviously considered possible.

The invention will be described with reference to the figures forming anintegral, non-limiting, component of the disclosure. The figures areintended to facilitate an understanding of the invention and are notintended to limit the invention in any way. Throughout the figuresvarious elements will be numbered accordingly.

Combining capacitors into groups is a common practice to improveelectrical performance. The combination typically exists in methods toincrease the electrical performance by combining discrete capacitorsinto commonly terminated arrays or stacks however, the limitations ofthe discrete capacitors in the array are not addressed. An example ofcombinations of capacitors is provided in U.S. Pat. No. 7,280,343, whichis incorporate herein by reference, where increased electricalperformance, such as increased capacitance, is achieved by using commoncurrent collecting parts to form single common anode and cathodeconnections. The present invention differs by creating multipleindependent cathode and anode connection points, for use by the enduser, as opposed to arrays or stacks of commonly terminated capacitiveelements. A stack of capacitive elements typically refers to combiningmultiple capacitors or capacitive elements into a single common cathodeand anode termination system, arranged in a pattern or in a stack, toachieved improved performance such as increased capacitance. Contrarily,distributing capacitance over a multitude of independent electricalconnection points in close proximity, with no common electricalconnection, as in the present invention, allows for reductions in theelectrical parasitics and allows for a reduction in the amount ofcapacitance needed thereby further advancing efforts related tominiaturization.

An embodiment of the invention is illustrated in top schematic view inFIG. 1. A portion of the embodiment of FIG. 1, taken along line 2-2, isillustrated in side schematic view in FIG. 2. A substrate, 101,comprising a conductive layer, 111, and a porous dielectric layer, 112,has formed thereon isolation material, 102, circumventing an area, 103,which will be formed into an active area after further processing. Theconductive layer preferably has a roughened surface to facilitate theformation of the dielectric and to increase surface area. As illustratedin FIG. 2, the isolation material extends through the dielectric andpreferably into the conductive layer to a depth sufficient to inhibitcathode material from wicking past or under the insulation material.Through diligent research it has been determined that a limitation withprior art capacitor arrays is reached when the cathode material wicksunder or around the isolation material such as through the dielectricunder the isolation material. Prior practice was to form the isolationmaterial on the surface of the dielectric which was considered adequate.The phenomenon of wicking under the isolation material was previouslyneither considered nor realized. It was not until continued efforts tominiaturize beyond that previously considered possible with barriersthat the problem of wicking was realized. The present invention allowsfor miniaturization beyond that previously considered possible, whenforming many capacitors in a close array.

Rectangular areas are illustrated in FIG. 1 for illustrative purposeswith the shape and number of areas being a design choice depending onthe number of capacitors to be formed, the size required for eachcapacitor and the desired capacitance as well known in the art. Theareas on a common substrate may be the same or different. Shapes otherthan rectangular are suitable for demonstration of the inventionincluding but not limited to, circular, curved, polygonal andcombinations thereof. Polygonal, such as triangular, rectangular,pentagonal, hexagonal and the like are preferred due to the increasedpacking density which can be achieved thereby. A mixture of shapes andsizes can be employed to achieve the highest density of capacitors withthe understanding that at least enough sides are included as to form acomplete boundary.

An embodiment of the invention will be described with reference to FIG.3 wherein provided is a partial cross-sectional schematic view. In FIG.3 the substrate, 101, and isolation material, 102, are as described inFIGS. 1 and 2. A cathode layer, 201, is formed within the area definedby the isolation material wherein the isolation material prohibitscathode material from passing through, under or around the isolationmaterial. The cathode material is therefore separated from theconductive layer, 111, by the dielectric, 112, which forms a capacitivecouple with an active area having a size and shaped defined by the areacircumscribed by the isolation material.

With continued reference to FIG. 3, a carrier film, 301, is applied tothe capacitor array, 104, so that it is in contact with at least aportion of each individual capacitor. The carrier film, 301, provides ananchor to each capacitor thereby forming a common structure which isstabilized by the carrier film. When the capacitors are individualizedby physical and electrical isolation of both the cathode and anode theyneed to have a common structure so as to retain the positional integrityof the capacitor array. The carrier film also provides a foundation forhandling multiple discrete capacitors. This carrier film can be appliedto either side of the capacitor, in contact with the cathode layers orin contact with the anode foil, as long as it contacts at least aportion of each capacitor so as to provide a common physical layer. Thecarrier film can be formed in many ways and of many materials includingbut not limited to adhesive film, adhesive tape, release film, a sprayedliquid that forms a film, spin coating, injection molding, or staticadhesion. The carrier film may also penetrate any portion of the array,including, the anode porous layer, space between isolating materials, orconductive cathode layers.

An embodiment of the invention will be further described with referenceto FIG. 4 wherein provided is a partial cross-sectional schematic viewillustrating two capacitive couples without limit thereto. In FIG. 4 theanode foil, 101, with the conductive layer, 111, which is the anode ofthe capacitive couple and dielectric layer, 112, are as discussed aboveas is the isolation material, 102. As a preferred but non-limitingembodiment of this present invention the conductive cathode layers, 201,are represented as three layers; a conductive polymer layer or manganesedioxide layer, 211, a carbon layer, 212, and a metal layer, 213. Thecarbon layer may be a carbon paint layer. The metal layer may be a metalpaint layer or a plated metal layer. It is understood for the purpose ofthis invention that the term “paint” includes any filled system thatcontains a binder agent and a conductive particle. Conductive paintlayers are preferred due to the specificity with which they can beapplied.

An embodiment of the invention is illustrated in schematiccross-sectional view in FIG. 5 wherein the carrier film, 301, is locatedon the cathode side of the array. A portion of the anode foil, 401, isremoved to form a substrate vacancy, 401. The capacitive couple, 601,comprising the anode, 111, dielectric, 112 and cathode, 201, is asdiscussed above. The method of forming the substrate vacancy is notparticularly limited with exemplary methods with suitable methods fordemonstrating the invention including, laser ablation, laser cutting,mechanical cutting, dicing, chemical etching, milling, ion milling,blast polishing, or the like. The method for forming the substratevacancy is selected based on the performance requirements needed fromthe capacitor array. The intent in forming the substrate vacancy is toelectrically isolate the common anode portion of the capacitors. Afterformation of the substrate vacancy the capacitive couples areelectrically individualized and the carrier film, 301, retains the arraystructure. Further cutting of the carrier film, 301, can be done tocreate smaller groups of arrayed capacitors. In one embodiment of thepresent invention a portion of the anode foil, 101, remains and extendsbeyond the boundary of the capacitive couple to function as an anodetab, 403. This anode tab, 403, can be created as a part of anindividualized capacitor so as to allow for electrical attachment. Inone embodiment the carrier film, 301, is a release layer. In use theindividual capacitors are released on to a separate substrate and theanode tab, 403, is exposed to provide a location for electricalconnection which can be on the same side of the individual devices asthe cathode connection.

Another embodiment of the present invention is represented in FIG. 6,wherein the carrier film, 301, further comprises a cathode foil, 702,which provides a bondable surface for the capacitors. An optionalcathode tab, 703, can be extended beyond the active regions as needed byapplication. The cathode foil, 702, can be attached to the conductivecathode layers, 201, by use of a metal filled adhesive, 701, or otherattachment methods as known in the art. Other methods suitable fordemonstrating the invention include, but are not limited to, a carbonfilled bonding layer, adhesion by a conductive polymer, soldering,welding, or any other method to electrically or physically attach thecathode foil, 702, to the conductive cathode layers, 201. As in the casewith the anode tab, 403, the cathode foil tab, 703, can be used for anelectrical connection to the cathode on the same side of the capacitoras the anode thereby providing a discrete capacitor. The cathode foilmay be a plated metal such as copper, silver or nickel.

An embodiment of the invention is illustrated in FIG. 7 wherein thecarrier film is applied to the anode foil. In the embodiment of FIG. 7 aportion of the carrier film, 301, can be slightly removed during theanode foil removal process. This will leave a slight indention, 801, ofremoved carrier film. This process will ensure that the physicalconnection remains with the carrier film but that the anode foil iscompletely isolated as to ensure that the array contains at least twoindividual capacitors. The indention may provide an easily severed area,such as a perforation, or to facilitate separating the primary arrayinto smaller arrays or individual capacitors.

An embodiment of the invention is illustrated in cross-sectionalschematic view in FIG. 8. In FIG. 8 the anode is treated to provide abond surface, 901, to facilitate electrical connection of the capacitorto a circuit. This treatment could include but is not limited totreating at least part of at least one surface by, plating, polishing,chemical etching, welding, fusing or bonding with the proviso that theintegrity of the dielectric remains.

An embodiment of the invention is illustrated in top view in FIG. 9. InFIG. 9 a primary array, 1001, of individual capacitors, 404, can behandled as an array or separated into sub-arrays, or individualcapacitors. This allows a large number of capacitors to be placed intoan application with a single process. Alternatively, a large number ofcapacitors can be transported for later use in sub-arrays or asindividual capacitors with the spatial orientation maintained.

An embodiment of the invention is illustrated as a partial top view inFIG. 10. In FIG. 10, a multiplicity of capacitors are provided whereinthe cathode, 201, circumscribed by the isolation material, 102, is on asubstrate, 301, with an anode tab, 403. The small array may be placed,as is, onto a circuit and electrically connected with the substratebeing removed or remaining.

The roughened surface of the conductive layer can be made by additive orsubtractive methods that are known in the industry, such as theelectrochemical etching of the foil or the formation of powder particlesof a valve metal or oxide of a valve metal sintered to a foil. Thedielectric typically mimics, at least in part, the undulations of theroughened surface.

The cathode layer may comprise multiple layers preferably selected fromlayers of conductive polymer, manganese dioxide, conductive carbon ink,conductive metal ink and the like. Other materials can be used to formthis conductive cathode layer including but not limited to, ionic salts,liquid electrolytes, or other suitable current conducting materials. Aswould be realized the isolating material restricts the location of thecathode material so as to create individual capacitive couples with adistinct cathode for each capacitive couple. It would also be understoodthat adjacent capacitive couples can be closely spaced allowingsufficient room to separate the individual capacitors if desired.

The method of forming the isolation material is not particularly limitedherein. Methods of forming this isolating material for demonstration ofthe invention include but are not limited to removal of the porous layerand application of an isolating material in the removed portion, or theisolating material only present in the porous layer. It is preferred touse the removal of the porous layer in combination of adding anisolating material so as to minimize wicking of the isolating material.By minimizing this wicking additional reduction in size can be achieved.

The method of electrically connecting the anode and cathode of thecapacitor array to a circuit trace are not particularly limited herein.Methods which are particularly suitable for demonstrating the inventioninclude, but are not limited to, through hole via connection,wire-bonding, soldering, welding, braising, plating, ultrasonic welding,laser welding or the like.

The carrier film can be located at any part of the capacitor array,provided it forms a structural support to physically connect, at leasttemporarily, capacitors in the array. Multiple carrier films can also beused either simultaneously or sequentially and can be attached to anyside of the array. Other possible uses for the carrier film can be atemporary structure for transferring the capacitor array. This can beachieve by the use of a material with releasing properties, such as butnot limited to, thermal release film, pressure release film, solublefilm, or other methods of removing the film once the capacitors havebeen transferred to the final placement. One preferred embodiment is theuse of two carrier film layers. One carrier film is a double sidedadhesive that bonds the capacitors in an array on one side and providesan adhesive surface for bonding the capacitors to a usable surface onthe other. Once that adhesive layer is in contact with both thecapacitors and the usable substrate, the second carrier film that is arelease film can be detached leaving the capacitors present on thedesired surface. In other embodiments the adhesive film is replaced byan adhesive applied to either the capacitors surface or the usablesubstrate.

The term isolating material describes any material that forms aphysical, chemical, or electrical barrier. This term may be interchangedwith masking material or damming material. It is understood in theindustry that this isolating material can be applied by many methods,such as but not limited to deposition, transfer, screen printing, orspray. It is also understood that this material prevents the cathodematerials from escaping beyond the boundaries created by this material.Part of this is accomplished by the isolating material penetrating intothe porous anode layer so that wicking within the porous layer is alsoprevented. It is also possible, but not integral, that the isolatingmaterial resides above the porous anode layer surface as to preventouter cathode materials from escaping beyond the boundaries. Theinvention has been described with particular reference to preferredembodiments without limit thereto. One of skill in the art would realizeadditional embodiments and improvements which are not specificallyenumerated but which are within the scope of the invention asspecifically set forth in the claims appended hereto.

The invention claimed is:
 1. An array of capacitors comprising; an anodefoil comprising a conductive layer and a porous dielectric layer on saidconductive layer of said anode foil; a multiplicity of areas on saidporous dielectric layer wherein each area of said areas is circumventedby an isolation material and said isolation material extends throughsaid porous dielectric layer and forms an isolation material layer onsaid conductive layer of said anode foil; a conductive cathode layer ineach said area forming a capacitive couple wherein said isolationmaterial does not extend over said conductive cathode layer; at leastone substrate vacancy in said anode foil wherein said substrate vacancyelectrically isolates adjacent anodes of adjacent capacitive couples;and a carrier film attached to said capacitive couples.
 2. The array ofcapacitors of claim 1 wherein said anode foil is a valve metal or oxideof a valve metal.
 3. The array of capacitors of claim 2 wherein saidanode foil comprises a roughened surface area on which said porousdielectric layer is formed.
 4. The array of capacitors of claim 1wherein said conductive cathode layers comprise at least one of anintrinsically conductive polymer or manganese dioxide.
 5. The array ofcapacitors of claim 1 wherein at least one said conductive cathode layercomprises at least one layer selected from the group consisting of acarbon paint layer, a metal paint layer, a plated metal layer and acathode foil.
 6. The array of capacitors of claim 5 wherein said anodefoil comprises an anode tab extending beyond said active capacitivecouple.
 7. The array of capacitors of claim 1 wherein said carrier filmcomprises at least one material selected from the group consisting of arelease film, adhesive film and coated layer.
 8. The array of capacitorsof claim 1 further comprising at least one cathode tab.
 9. The array ofcapacitors of claim 1 wherein said anode foil comprises a bond surfaceelectrically connected to an anode tab.
 10. The array of capacitors ofclaim 1 wherein said isolation material extends into said conductivelayer to a depth sufficient to inhibit cathode material from wickingpast or under said isolation material.
 11. An array of capacitorscomprising; a valve metal foil comprising a conductive layer and aporous dielectric layer on said conductive layer of said valve metalfoil; a multiplicity of areas on said porous dielectric layer whereineach area of said areas is circumvented by an isolation material andsaid isolation material extends through said porous dielectric layer andforms an isolation material layer on said conductive layer; a conductivecathode layer in each said area forming a capacitive couple wherein saidisolation material does not extend over said conductive cathode layer;at least one substrate vacancy in said valve metal foil wherein saidsubstrate vacancy electrically isolates adjacent anodes of adjacentcapacitive couples; and a carrier film attached to said capacitivecouples.